Treatment of pigment surfaces is a well-known art in the field of coating, cosmetic and ink technology. Usually it involves adsorbing a surface-modifying agent such as polymer, surfactant, oil, etc., to pigment surfaces through dispersing the pigment in a liquid vehicle. The conventional dispersing (or grinding) equipment, for example, are three-roll mills, stone and colloid mills, and high-speed impingement mills. The conventional art of pigment dispersion is taught in a textbook by T. C. Patton, titled "Paint Flow and Pigment Dispersion", 2nd edition, Wiley Interscience, New York, 1978.
Fluidized-bed technology has been reported in U.S. Pat. No. 4,264,552 as a successful technique for treating pigments wherein certain types of granulating assistants for the process are disclosed. One of the types of granulating assistants disclosed in this patent as being useful is a water-soluble polymeric agent.
We have discovered an improvement in the fluidized bed process for treating pigments utilizing certain water-dissipatable polyesters as hereinafter described, wherein the treated pigments have improved properties.